(nb: I set a breakpoint with "debugger" instruction)
If I happen to step over (F6) or step into (F5) on the last instruction it deadlocks, leaving 8 threads with a similar stack waiting for a critical section owned by main runner thread.
They are waiting there :

Unfortunately what you're seeing now is the effect of a
V8 bug. Currently, if you "Step Over" the final line of a script, the V8 runtime and the Eclipse-based debugger get out of sync; the debugger believes the application is now running, but the V8 runtime encounters an internal error, reports it
to the debugger, and remains stopped. Until this is fixed, you must use "Resume" to continue past the final line of a script.

Thanks for testing our fix! We'll incorporate it into ClearScript's next release. And thanks again for reporting that bug; it was a very subtle one that could cause both deadlocks and memory corruption.